1. Field of the Invention
The present invention relates in general to cast abrasion resistant hollow balls and more particularly to a hollow pulverizer ball formed on a hollow ceramic core.
2. Description of the Related Art
Hollow metallic balls for pulverizer use have been known where a core hole has been provided in the wall of the ball to discharge any gases evolved in the casting process. Ordinarily, the opening or core hole in the wall of the cast ball has generally been closed by means of a plug or the like.
U.S. Pat. No. 3,254,849 relates to a cast hollow ball which utilizes a core that is consumed in the metal casting process. Gases evolved during the solidification of the metal within the mold escape from the interior of the ball through openings in the arms or radial pipe-like spokes. This patent teaches that the spokes or arms are advantageously hollow with both ends open so that the gases evolved during solidification of the metal will discharge through the hollow arms of the spider.
It is well known that pulverizer balls must be hollow to allow for the dissipation of compressive forces internally which prevent excessive breakage and service.
Still there exists a need for a process which solves problems associated with the prior art processes. These problems include the core moving due to ferrostatic forces acting thereon. Also, there is a problem with the possibility of fractures initiating at the supports that cause premature failure of the ball with the prior art process. There is need for a process that eliminates the formation of gases in the interior of the casing which can impact the casting integrity and causing premature failure. Also there is a need for a process that eliminates the possibility of metal penetrating the center core material which can contribute to out of balance condition which eventually also leads to premature failure. Thus, there is a need for a new process for making cast abrasion resistant hollow balls and also a need for a cast abrasion resistant hollow ball which has a longer life than the prior art cast hollow balls.